Age and origin of Pan-African granites and associated U-Mo mineralization at Ekomédion, southwestern Cameroon

Various granites in the Pan-African Neoproterozoic Fold Belt of Cameroon were investigated in an area around Ekomédion (southwestern Cameroon) in order to set constraints on their genesis and age. The studied granites were likely emplaced in relation with the Central Cameroon Shear Zone (CCSZ). Hence dating the granites provides an age for the dextral transcurrent tectonics event responsible for the CCSZ. The interest in these granitic rocks is spurred by noticeable Mo and U mineralization in a pegmatite that is hosted by two-mica granite. The studied granites comprise post-collisional syn-D4 two-mica granite, alkali-feldspar granite, biotite-rich granite and porphyritic granite. Based on lithogeochemical data, the granites can be characterized as ferroan, peraluminous and high-K calc-alkaline. The biotite-rich and alkali feldspar granites show I-type characteristics, whereas the porphyritic and two-mica granites reveal S-type affinity. All of them are marked by strong light rare earth element fractionation and a strong negative Eu anomaly, and they are strongly depleted in Ba, Nb, P, Sr and Ti, pointing to a crustal origin. Crust assimilation is also evident from zircon xenocrysts in the two-mica granite with upper intercept U-Pb ages of 2051 ± 44 Ma and 1550 ± 24 Ma. U-Pb dating of zircon, monazite and xenotime grains/domains yielded indistinguishable ages for both the two-mica granite (578 ± 4 Ma) and the porphyritic granite (579 ± 3 Ma). An identical age (578 ± 11 Ma) was obtained by Re-Os dating of molybdenite that occurs together with uraninite in pegmatite within the two-mica granite, thus clearly attesting to a late-magmatic origin of the ore. The studied granites have many similarities, both in composition and age, with granites in Nigeria and northeastern Brazil, supporting the continuation of a large Pan-African/Braziliano magmatic province from west-central Africa to northeastern Brazil.